#include <iostream>
#include <cmath>

#define PI 3.14159265

double area(double radius=0);
double area(double a, double b);
double area(double a,double b,double h);
double area(double a,double b,double c,int);

//带有缺省函数
double area(double radius)
{
    return PI*radius*radius;
}

double area(double a, double b)
{
    return a*b;
}

double area(double a,double b,double h)
{
    return 0.5*(a+b)*h;
}

double area(double a,double b,double c,int)
{
    double s =0.5*(a+b+c);
    return sqrt(s*(s-a)*(s-b)*(s-c));
}

